When attempting to separate particulate matter from a fluid, it is known that very small (slowly settling) particles are exponentially more difficult to separate by centrifugation than larger particles. Accordingly, most disc-type centrifuges are designed to spin at extremely high speeds in order to separate the smallest particles at a reasonable rate. High speeds mean high stress on the equipment and on the particulate matter being separated. On the other hand, it is not always necessary for a centrifuge to be capable of separating extremely small particulate matter, especially if the operator is only interested in larger material.
However, there has not been any consideration given in the past to a disc-type centrifuge dedicated to larger particle separation such that the centrifuge could operate at relatively low speeds, resulting in less stress on the equipment and permitting the utilization of less exotic construction material and techniques.
Commonly assigned Canadian patent application Ser. No. 579,008 filed Sep. 30, 1988 discloses and claims a low speed particle concentrator or centrifuge which overcomes the above-enumerated problems. That device includes as a feature thereof a mechanism for controlling the particulate outflow by controlling or adjusting the operating gap between the upper and lower bowls thereof. Adjustment is effected manually, by rotating an adjusting nut relative to the upper bowl member, the nut defining or setting an upper limit to the available upwards movement of the upper bowl member. The mechanical adjustment must be effected while the concentrator is at rest.
There are instances and circumstances which necessitate, or at least make it desirable, to have automatic or powered adjustment of the inter-bowl gap available. For example it may be desirable to have the gap increase automatically at preset intervals of time to flush out oversized particles, or to change back and forth between different gap settings for culture mode and separation mode as in semi-continuous culture. Also, after the device has been stopped completely the impeller pump must be re-primed, further complicating the procedure for automated adjustment.